Vehicle operators routinely encounter vehicle situations in which a decision is required or advisable to take action, either by performing a vehicle control action or by refraining from performing an intended vehicle control action, in order to avoid an undesirable event; but a vehicle operator may not become aware of such a situation in time for the optimal action.
For example, an operator of a first vehicle may be driving in a lane of a multi-lane roadway when a second, faster moving vehicle in an adjacent lane approaches from the rear. This does not by itself require any action by the first vehicle operator, as long as the operator is not planning to change lanes into the lane occupied by the overtaking second vehicle. But if the operator of the first vehicle is intending to change lanes into that occupied by the overtaking second vehicle, a collision might occur when that action is taken. The operator of the first vehicle, before changing lanes, may check a rear view mirror to determine if any vehicles are present in the destination lane. But most vehicles have a “blind spot,” in which another vehicle cannot be easily seen with such a mirror check. Thus, it has been suggested to provide a detector, based on radar or a similar technology, to detect a second vehicle in the adjacent lane and alert apparatus responsive to such detection to provide an alert to the operator of the first vehicle of the presence of a second vehicle. An operator may consider such a detector useful as a backup to his own driving procedures. But most of time the operator of the first vehicle has no intention of changing lanes; and for such times the operator may consider the repeated activation of the alert signal may to be useless and annoying.
Another example of such a vehicle situation is a person, animal, second vehicle or other object that appears on the road in the projected path of the first vehicle. An alert operator of the first vehicle will normally see the potential for collision with the object and brake and/or steer to avoid it; but an operator of the first vehicle who is distracted might be looking away from the road ahead and miss the chance to avoid collision. An external object detector directed toward the projected path of the vehicle may activate an alert device to bring the attention of the first vehicle operator back in time to avoid the collision. But, once again, alert signals generated by the presence of preceding vehicles may be similarly annoying when the vehicle operator of the following vehicle is looking ahead and already aware of them.